Auto merge of #56117 - petrochenkov:iempty, r=eddyb

resolve: Make "empty import canaries" invisible from other crates

Empty imports `use prefix::{};` are desugared into `use prefix::{self as _};` to make sure the prefix is checked for privacy/stability/etc.
This caused issues in cross-crate scenarios because gensyms are lost in crate metadata (the `_` is a gensym).

Fixes https://github.com/rust-lang/rust/issues/55811

src/test/ui/imports/auxiliary/issue-55811.rs

@@ -0,0 +1,5 @@
+mod m {}
+
+// These two imports should not conflict when this crate is loaded from some other crate.
+use m::{};
+use m::{};

src/test/ui/imports/issue-55811.rs

@@ -0,0 +1,6 @@
+// compile-pass
+// aux-build:issue-55811.rs
+
+extern crate issue_55811;
+
+fn main() {}